Heidi Klum's bodyguard boyfriend plays the dotin

Heidi Klum rang in her 40th birthday with a fun family weekend.

The supermodel, who reached the milestone on Saturday, continued the celebrations on Sunday with a breakfast at Shutters On The Beach in Santa Monica.

Her bodyguard boyfriend Martin Kristen played the doting step-dad as they later strolled along the beach front, cradling little Lou, three, in his arms.

Birthday fun: Heidi Klum and Martin Kristen take a stroll by the beach with her children Lou, Henry, and Johan in Santa Monica on Sunday

Doting: Martin cradled the supermodel's youngest daughter in his arms

The day before, Heidi had hosted hat-themed bash at her home in LA with guests including Black Eyed Peas singer Fergie. 

While she was no doubt lavished with gifts, her favourite was a personalised present from her children, Leni, eight, Henry, seven, Johan, six, and Lou - a frame of four painted moulds of their hands.

The America's Got Talent judge, who is well known for her love of dressing up and costume parties, previously revealed she was really 'excited' about turning 40 and wearing 'crazy' headwear at her party.

She said: 'I'm excited. My friend is actually throwing a party for me and it's going to be a hat party.

'I can't wait! We'll be having burgers, ice cream, fries, chocolate. All the usual stuff.

'Everyone has to show up in hat. So it's all girlfriends of mine and everyone has to wear a crazy hat. So we're all going to sit around with some hats on, which I think is fun.'

Heidi also admitted she isn't concerned with getting older, choosing to embrace the fact she's 'still here' enjoying life.

She added: '40 is the new 30. I don't really care about aging. I'm happy. When I get one year older it means we're still here, having a good time.'

The Germany's Next Top Model host kicked off her birthday celebrations earlier in the week when the show's hopefuls presented her with a chocolate cake.

Heidi has been in a relationship with her bodyguard since September.

The supermodel was married to stylist Ric Pipino for around five years and, after a brief romance with Flavio Briatore - Leni's father - she tied the knot with musician Seal in May 2005. They separated in January 2012.